As Kinessa try to juke him. An easy way to do that is to jump to the left/right between your shots. But zoom out when your jumping so you have more movement speed!
You should put a mine at your current position or at a point where you know he MUST come around. As you hear your mine you have 2 choices: 1.you kill him 2.you use your teleport to get away I would recommend to teleport to/near your team.
If RMB, you Reversal. Reversal will reduce Lex to low HP. You should always pick the Dark Stalker card. A good way to counter him Is to just out-damage him. You survive more shots than he.